Reliability, Validity, and Optimal Cut-Off Scores of Action Research Arm Test and Jebsen–Taylor Hand Function Test in People with Parkinson’s Disease

<b>Background/Objectives</b>: Although upper extremity dexterity problems are frequently reported in people with Parkinson's disease (PwPD), valid and reliable scales for assessing upper extremity function and dexterity are limited. The objective of this study was to investigate the reliability and validity of the Action Research Arm Test (ARAT) and the Jebsen-Taylor Hand Function Test (JTHFT) in PwPD. <b>Methods</b>: Seventy PwPD and thirty HC were recruited. The test-retest reliability was evaluated by determining the intraclass correlation coefficient (ICC). MDC₉₅ was calculated by using ICC results. The concurrent validities of JTHFT and ARAT were determined by investigating their relationship with the Nine-Hole Peg Test (9-HPT), Hoehn and Yahr scale (H & Y), Unified Parkinson's Disease Rating Scale (UPDRS), and motor symptoms (UPDRS-III). The cut-off times that best discriminated between PwPD and HC were investigated by plotting receiver operating characteristic (ROC) curves. <b>Results</b>: The ARAT and JTHFT showed excellent test-retest reliability (ICC = 0.937 to 0.995). The MDC₉₅ values for the ARAT were 0.38 for the dominant hand and 0.58 for the non-dominant hand. MDC₉₅ values for the JTHFT subtests and total scores ranged from 0.38 to 4.71. The ARAT, JTHFT subtests, and total scores demonstrated a fair-to-strong correlation with other outcomes (<i>p</i> < 0.05). The cut-off times that best differentiated JTHFT subtests and total scores ranged from 3.56 to 64.23. <b>Conclusions</b>: The JTHFT is a reliable and valid measurement tool for the assessment of manual dexterity in PwPD, while the ARAT is a reliable assessment tool in PwPD but does not have discriminant validity.